Process for preparation of bis-(beta-hydroxyethyl) terephthalate



n ted. S WSPWM 3,313,844 Patented 11;

, PROCESS FOR PREPARATION OF BIS-(B-HY- DROXYETHYL) TEREPHTHALATE Seikichi Matsuhisa, Numazu-shi, Shiznoka-ken, and Yoshio Miyama and Tadao Tsutsumi, Mishima-shi, Shizuoka-ken, Japan, assignors to Toyo Rayon Kabushiki Kaisha, Tokyo, Japan, a corporation of Japan 7 N Drawing. Filed Sept. 17, 1963, Ser. No. 309,389

Claims priority, application Japan, Sept. 24, 1962, 37/ 11,827; Oct. 19, 1962, 37/46,311 10 Claims. (Cl. 260-475) This invention relates to a process for preparation of bis-(,B-hydroxyethyl) terephthalate from terephthalonitrile, ethylene glycol, and Water, While preventing coloration of the product which heretofore cannot be avoided. More particularly, the invention relates to a process for preparation of bis-(B-hydroxyethyl) terephthalate, which comprises reacting terephthalonitrile, ethylene glycol, and Water at a temperature of l00300 0, preferably 180- 280 C., in .the presence of an esterification catalyst, with the addition to the reaction system of at least one coloration inhibitor selected from the group consisting of phosphoric acid, phosphorous acid, inorganic phosphates, inorganic phosphites, phosphoric acid esters, phosphorous acid esters, sulphur, inorganic sulphides, organic sulphides, inorganic sulphites, mercaptans and thio-organic acids.

In the past, many methods are known for the production of bis-(fl-hydroxyethyl) terephthalate, among which those industrially employed at present utilize ester-interchange reaction between dimethyl terephthalate and ethylene glycol, or esterification of terephthalate acid with ethylene glycol. Again, as a process for synthesizing bis-(,8- hydroxyethyl) terephthalate by a single step from the reaction of terephthalonitrile, ethylene glycol and water, British Patent No. 800,875 is known, which is based on the following Formula 1.

The same atent teaches that when terephthalonitrile, water, and et ylene glycol are mixed at the quantitative ratios of:

Ethylene glycol 5-10 mo-l/mol of nitrile group. Water l mol/mol of nitrile group.

NCCN 2HOCHzCH2OH zrno noomornooo-Q-ooocizwmon 2NH3 I For production of terephthalonitrile, recently a process 1 of air-oxidation of p-xylene at gaseous phase in the presence of ammonia is developed.

We made extensive studies and experiments in search for a process for an advantageous production of bis-(fihydroxyethyl) terephthalate while preventing the heretofore inevitable coloration of the product, and as the result found that by carrying out the reaction in the reaction system wherein at least one coloration inhibitor selected from the group consisting of phosphoric acid, phosphorous acid, inorganic phosphates, inorganic phosphites, phosphoric acid esters, phosphorous acid esters, sulphur, inorganic sulphides, organic sulphides, inorganicsulphites,

mercaptans and thio-organic acids, is present, the colora I by reacting terephthalonitrile, ethylene glycol and water tion phenomenon can be effectively prevented and bis-(fi-I hydroxyethyl) terephthalate of markedly improved quality can be obtained. Still further, it was found that the utility of the present process is not limited to the cases wherein the conventional esterification catalysts are used, but it is also useful in the reaction of the aforesaid Foirnula 1 using a novel catalyst previously proposed by us, which is composed of at least one metallic compound selected from the group consisting of oxides and salts of copper, zinc, cadmium, mercury, nickel, manganese and cobalt.

It is a well known fact that, generally in the formation of polyesteramides, use of free amine causes coloration of the product. For example, T. M. Laakso and D. D. Reynolds, J.A.C.S. 82 3640 (1960) discloses such. The coloration seen in the synthesis of bis-(,B-hydroxyethyl) terephthalate from terephthalonitrile, ethylene glycol, and water, is assumed to be caused by the same mechanism as of the said coloration of polyesteramide, but it is not yet completely understood.

Therefore, the object of the present invention is to provide a process for production of bis-(fl-hydroxyethyl) terephthalate whereby, in the synthesis of bis-(,8-hydroxy ethyl) terephthalate by reaction of terephthalonitrile, ethylene glycol, and water under the presence of an esterification catalyst, the heretofore inevitable coloration of the product can be effectively prevented with industrial advantages.

Other objects of the invention will become clear by reading the rest of the specification.

The above object of the invention can be accomplished in the presence of an esterification catalyst, at a temperature within the range of l00300 0, preferably 180- 280 C., with the addition to the reaction system of at least one coloration inhibitor selected from the group consisting of phosphoric acid, phosphorous acid, inorganic particularly l280 CZ phosphates, inorganic phosphites, phosphoric acid esters, phosphorous acid esters, sulphur, inorganic sulphides, organic sulphides, inorganic sulphites, mercaptans and thio-organic acids.

According to the invention, bis-(fi-hydroxyethyl) ter:

ephthalate of excellent color tone can be prepared while,

preventing heretofore inevitable coloration'phe'nomenon, without any adverse effect on the conversion ratio of terephthalonitrile to bisetfl-hydroxyethyl) terephthalate.

.As the catalyst in the process of the invention, besides those esterification catalysts known as having catalytic ability in'the reaction of the Formula 1, e.g., hydroxides of alkali metals and alkali earth metals, weakly acid salts, and basic compounds such as pyridine and ammonia, other novel catalyst composed of one or more of compounds selected from oxides and salts of copper, zinc, cadmium, mercury, nickel, manganese and cobalt can be used. As such metallic compound, any of the oxides, inorganic and organic acid salts of the aforesaid metals may b used l,

According to the invention, bis-(,B-hydroxyethyl terephthalate can be produced with "high efliciency while advantageously preventing the coloration of the product in the presence of either the novel catalysts mentioned above, or those known catalysts heretofore used in the reaction of the foregoing Formula 1.

According to the invention, for practice it is preferred to use terephthalonitrile, ethylene glycol and water by the following ratios, that is, in terms of mol ratio, ethylene glycol to nitrile group of 2-12, particularly 5-10, and water to nitrile group, 0.5-5, particularly about 1, and to make the reaction temperature about l00300 C., The reaction may be carried out under atmospheric-pressure or elevated pressure.

Again the process ofthe invention is also applicable generally for synthesis of ester by reaction of nitrile with alcohol and water.

As the coloration inhibiting agent useful for the invention, besides phosphoric acid, phosphorous acid, and sultube, together with 0.1 g. of cadmium acetate as a catalyst and 0.1 g. of phosphoric acid as a coloration inhibitor. The flask was then heated under reflux in 220 C. oil bath, while nitrogen saturated with water being phur, may be named are: inorganic phosphates such as 5 simultaneously introduced thereinto. The formed amcadmium phosphate, calcium phosphate, sodium phosmonia was led to a 1,000 ml. absorption bottle filled phate and zinc phosphate; inorganic phosphites such as with 1 N sulfuric acid from the front end of the reflux cadmium phosphite, calcium phosphite, sodium phoscondenser, and absorbed there. After the reaction, the phite, potassium phosphite, and copper phosphite; phosconversion ratio was calculated by back-titration with an phoric acid esters such as triphenyl phosphate, trimethyl aqueous solution of sodium hydroxide. The conversion phosphate, tributyl phosphate, dibutyl hydrogen phosratio after 5 hours of the reaction was 95.2%. When phate and trihexyl phosphate; phosphorous acid esters the degree of coloration of the reaction liquid was meassuch as tributyl phosphite, trihexyl phosphite, diethyl ured at 150 C., its H'ztzen number was 60.

phosphite, triethyl phosphite and monoethyl phosphite;

. Control 1 inorganic sulphides such as sodium sulphide, zinc sulphide, ammonium sulphide, diphosphorus pentasulphide, For compaflson, Example 1 was repeated lead sulphide, calcium sulphide, copper sulphide, except that the coloration inhibitor was not added. The mium sulphide, Sodium polysulphide, ammonium polyconversion ratio after the 5 hours similar heating unsulphide and potassium polysulphide; organic sulphides f reflux Was a the reaction liquid was yellow such as benzyl sulphide, diphenyl sulphide, tetramethyl- 15h brown; havmg a Hazen number of more than thiuram disulphide, fl-naphthyl disulphide, thioanisole, M L 2 ethyl sulphide and methyl sulphide; inorganic sulphites such as sodium sulphite, zinc sulphite, calcium sulphite, 'test.tube provlded with a reflux condenser and a cobalt sulphite, sodium hydrogen sulphite and potassium l f Inlet tube was charged 2 of terephthalo' hydrogen sulphite; mercaptans such as methylmercaptan, mmle f ethylene glycol of Water ethylmercaptan, thiophenol; and thio-organic acids such of cupnc chlonde as l y and of cadmmm as thiosalicyclic acid, thiobenzoic acid, dithiobenzoic acid phosphate as a t mhlbltoll' The b was then andvthiwacetic acid heated under reflux in 220 C. oil bath while nitrogen In the process of the Present invention, the amount saturated with water being simultaneously introduced of use of such a coloration inhibitor is not particularly Thus formed ammoma was 3 l a 100 Critical however, normally it is from about by absorption bottle filled with 1 N sulfuric acid from the weight to the terephthalonitrile used. In order. to add from of the reflux .conderlser and absorbed After the coloration inhibitor to the reaction system and cause h l l the Converslon was calclllated by a its concurrent presence therein, the inhibitor may be mratlon h an aqueous sohmon of sodmln hydroxlde' added to the reaction material-s before the reaction, or The converslog ram) after 5 hours of heatlng under remay be added to the reaction system at the optional stage flux 2 h i degree 9 coloratlon measured of the reaction. However, it is generally preferred that at 150 was 70 m Hazen number thesame be present in the reaction system prior to the EXAMPLES 315 initiation of the reaction. U h

In the following, several embodiments of the present 0 p i same reactor i' m Example the cobra invention will be explained with reference to examples m lblt-mgdfifiegts of val-lous-phospho-rps compounds and controls for comparison purpose, it being understood i? examme the fcinowmg condmons' The rehowever that the present invention of course should not su S were as 8 own Tab e below l p rebe limited thereby sult of the same experiment without the addition of any coloration inhibitor is shown as Control 2.

EXAMPLE 1 Reactants: The following reactants, that is, Terephthalommle 2 Ethylene glycol g 9.8 Terephthalonitrile 20 later Ethylene glycol 98 Catalyst. "7".? Water 6 Coloration inhibitor g 0.01

Reaction conditions: were charged to a 500 ml. three-necked flask equipped Bath temperature C 200-220 with a reflux condenser, a stirrer, and a nitrogen inlet Reaction period hrs 5 TABLE 1 Catalyst Coloration inhibitor rati% i e i c gi it) gl aft i ri (Hazen number) 5223 21 iu t y at 87.8 i

3 Cadmium acetate Tributyl phosphite 84.6 50 do Tr 1hexy1ph0sphite- 95.6 '80 d Dibhugyl hydrogen phos- 81.6

p l e. do Triphenyl phosphate. 92. 3 Zinc acetate. Trunethyl phosphate. 85. 6 40 do. Phosphorous aeid 85. 8 Trica1eiumphosphate 90.9 40 ..do Calcium hypophosphitem 84.8 80 Ouprous chloride Tril exyl phosphite 90.6 Cupric chloride Sodium pyrophosphate 77.1 100 Nickclformate Dlbfiltyl hydrogen phos- 82.2 90

Manganese formate Tr ihexyl phosphite 62.4 40 Cobalt acetate Tr1phenylph0sphate 89.6 60

1 Yellowish brown.

reaction mixture was heated to C.

N o'rE.-In the above Table 1, the degree of coloration (Hazen number) is the result of measurement when the 'Control 3 Reactants: I v

A 500 ml. three-necked flask equipped with a reflux gi i "75" condenser, a stirrer, and a nitrogen inlet tube was charged W y ene g yco with 20 g. of terephthalonitrile, 98 g. of ethylene glycol, ate'r 6 g. of water, and 0.1 g. of cadmium acetate as a catalyst, C t and heated under reflux in an oil bath of 220 C. while Q f mhlbltol L simultaneously nitrogen saturated with water being in- Reactlon Condltlons! troduced thereinto. The formed ammonia was led to Bath temperature C 200-220 a 1,000 ml. of absorption bottle filled with 1 N sulfuric Reaction period hrs 5 TABLE 2 Conversion Degree of Catalyst Coloration inhibitor ratio (percent) coloration (Hazen number) Control4 Sodium methylate 87.8 Example No.2

Thiophenol 95. 2 50 Ethyl rnercapta 92. 7 50 Dibenzyl sulphidea 81. 1 60 Thiosalicylic acid 88. 2 60 Sodium sulphide 83. 2 80 do Ammonium polysulphide. 79. 6 40 Sodium acetate Sulphur 96.4 70 Magnesium acetate Tetramethylthiuram di- 86. 2 70 sulphide. Cadmium acetate Zinc sulphide 87. 5 60 d Sodium sulphite. 90. 4 80 Zinc sulphide 92. 2 100 Dibenzyl sulphide. 82. 6 90 Sodium sulphide 90. 9 120 "do Thiosalicylic acid 86. 1 40 Cobalt acetate Sodium sulphite 83. 7 60 1 Yellowish brown.

Nora-In the above Table 2, the degree of coloration (Hazen number) is the result of measurement when the reaction mixture was heated to 150 C.

acid from the front end of the reflux condenser and absorbed there. After the reaction was completed, the conversion ratio was calculated by means of a backtitration with an aqueous solution of sodium hydroxide.

The conversion ratio after 5 hours of heating under reflux was 99.8%, and the reaction liquid was yellowish brown in color.

EXAMPLE 16 The experiment of Control 3 was repeated except that 0.1 g. of sulphur was added to the reactants as the coloration inhibitor.

After 5 hours of reaction, the conversion ratio was 96.4%, and the degree of coloration was 60 in Hazen number, when measured at 150 C.

EXAMPLE 17 A test tube equipped with a reflux condenser and a nitrogen inlet, tube was charged with 2 g. of terephthalonitrile, 9.8 g. of ethylene glycol, 0.6 g. of water,-0.01 g. of magnesium acetate, and 0.01 g. of thiophenol as the coloration inhibitor, and heated under reflux in an oil bath of 220 C., while nitrogen saturated with water being simultaneously introduced thereinto.

The formed ammonia was led to a 100 ml. absorption bottle filled with 1 N sulfuric acid from the front end of the reflux condenser, and absorbed there. After the reaction was completed, the conversion ratio was calculated by means of a back-titration with an aqueous solution of sodium hydroxide. The conversion rat-i0 after 5 hours of heating under reflux was 87.1%, and the degree of coloration was 50 in Hazen number, when measured at 150 C.

EXAMPLES 18-32 Using the same reactor used in Example 17, the coloration inhibiting eifects of various sulphur compounds were examined under the following conditions. The results were as shown in Table 2 below. Further, the result of the same experiment without the addition of any coloration inhibitor is shown as Control 4.

As is all the more clear from the results of Tables 1 and 2, according to the present invention, it is possible to produce bis-(fl-hydroxyethyl) terephthalate industrially with advantage, while preventing the heretofore inevitable coloration phenomenon.

What is claimed is:

1. Process for preparation of bis-(fi-hydroxyethyl) terephthalate which comprises reacting terephthalonitrile, ethylene glycol and water in the presence of an ester-ification catalyst, at a temperature of -300 C., with addition to the reaction system and co-presence therein of at least one coloration inhibiting agent selected from the group consisting of phosphoric acid, phosphorus acid, inorganic phosphates, inorganic phosphites, lower alkyl and phenyl esters of phosphoric acid, lower alkyl esters of phosphorous acid, sulphur, inorganic sulphides, organic sulphides selected from the group consisting of benzyl sulphide, tetramethylthiuram disulphide, fl-naphthyl disulphide, thioanisole, ethyl sulphide, diphenyl sulphide and methyl sulphide, inorganic sulphites, mercaptans selected from the group consisting of lower alkyl mercaptans, thiophenol and benzylmercaptan, and thio-organic acids selected from thiosalicylic acid, thiobenzoic acids, and thioacetic acid.

2. The process of claim 1 wherein said coloration inhibiting agent is added in an amount of about 0.01-1% by weight to the terephthalonitrile.

3. The process of claim 1 wherein said inorganic phosphate is at least one compound selected from the group consisting of cadmium phosphate, calcium phosphate, sodium phosphate and zinc phosphate.

4. The process of claim 1 wherein said inorganic phosphite is at least one compound selected from the group consisting of cadmium phosphite, calcium phosphite, sodium phosphite, potassium phosphite, and copper phosphite.

5. The process of claim 1 wherein said phosphoric acid ester is at least one compound selected from the group consisting of triphenyl phosphate, trimethyl phosphate, tributyl phosphate, dibutyl hydrogen phosphate and trihexyl phosphate.

6. The process of claim 1 wherein said phosphorous acid ester is at least one compound selected from the group consisting of tributyl phosph-ite, trihexyl phosphite, diethyl phosphite, triethyl phosphite and monoethyl phosphite.

7. The process of claim 1 wherein said inorganic sulphide is at least one compound selected from the group consisting of sodium sulphide, zinc sulphide, ammonium sulphide, diphosphorus pentasulphide, zinc sulphide, calcium sulphide, copper sulphide, cadmium sulphide, sodium polysulphide, ammonium polysulphide and potas sium polysulph-ide.

8. The process of claim 1 wherein said inorganic sulphite is at least one compound selected from the group consisting of sodium sulphite, zinc sulphite, calcium sulp'hite, cobalt sulphite, sodium hydrogen sulphite and potassium hydrogen sulphite.

9. The process of claim 1 wherein said mercaptan is References Cited by the Examiner UNITED STATES PATENTS 2,650,213 8/ 19'53 Hofrichter 260--75 2,921,088 1/1960 Gasson et a1 260475 3,171,828 3/1965 Isaacs et al 260475 LORRAINE A. WEIN'BERGER, Primary Examiner.

R. K. JACKSON, T. L. GALLOWAY,

Assistant Examiners. 

1. PROCESS FOR PREPARATION OF BIS-(B-HYDROXYETHYL) TEREPHTHALATE WHICH COMPRISES REACTING TEREPHTHALONITRILE, ETHYLENE GLYCOL AND WATER IN THE PRESENCE OF AN ESTERIFCATION CATALYST, AT A TEMPERATURE OF 100-300*C., WITH ADDITION TO THE REACTION SYSTEM AND CO-PRESENCE THEREIN OF THE LEAST ONE COLORATION INHIBITING AGENT SELECTED FROM THE GROUP CONSISTING OF PHOSPHORIC ACID, PHOSPHORUS ACID, INORGANIC PHOSPHATES, INORGANIC PHOSPHITES, LOWER ALKYL AND PHENYL ESTERS OF PHOSPHORIC ACID, LOWER ALKYL ESTERS OF PHOSPHOROUS ACIDS, SULPHUR, INORGANIC SULPHIDES, ORGANIC SULPHIDES SELECTED FROM THE GROUP CONSISTING OF BENZYL SULPHIDE, TETRAMETHYLTHIURAM DISULPHIDE, B-NAPHTHYL DISULPHIDE, THIANISOLE, ETHYL SULPHIDE, DIPHENYL SULPHIDE AND METHYL SULPHIDE, INORGANIC SULPHITES, MERCAPTANS SELECTED FROM THE GROUP CONSISTING OF LOWER ALKYL MERCAPTANS, THIOPHENOL AND BENZYLMERCAPTAN, AND THIO-ORGANIC ACIDS SELECTED FROM THIOSALICYCLIC ACID, THIOBENZOIC ACIDS, AND THIOACETIC ACID. 